1. Field of Invention
The present invention relates to a method of manufacture and apparatus for an improved efficiency large area flat fluorescent lamp. More particularly, the present invention utilizes waveguiding spacers, closed hollow electrodes and an internal dielectric mirror to achieve improved brightness, greater uniformity of brightness and longer life.
2. Description of the Prior Art
The technology of small portable video screens is continuously improving. Bulky cathode ray tube screens are increasingly being replaced by low weight flat screens. One popular video screen utilizes liquid crystal display technology. Most liquid crystal displays used in computer terminals, portable televisions and video phones depend on a backlighting source to display high quality information and images. Prior art backlighting sources employ various designs in which the primary source of light is from conventional tubular fluorescent lamps.
Both as an improvement over the tubular fluorescent backlight design and to meet the size and thickness requirements of liquid crystal displays, the need for a flat fluorescent lamp backlight design arose. One prior art technique uses two electrodes on opposite ends of a flat fluorescent lamp. See K. Hinotani, S. Kishimoto, K. Terada, "Flat Fluorescent Lamp for LCD Backlight", International Display Research Conference 52-55, 1988. This design employs a single discharge channel consisting of two discrete hollow electrodes running the entire length of each side of the lamp.
Although the Hinotani et al. design represents an improvement over the tubular fluorescent lamp backlight design, the problems of substantial light loss and non-uniformity of brightness are still present. Light loss in the Hinotani et al. backlight can be attributed to several factors including the use of substrate spacers that are inefficient light waveguides. Further loss of light can be attributed to absorption of visible light by the rear substrate glass. This loss of light occurs because the aluminum reflecting film is disposed on the external surface of the rear substrate. A portion of the generated light is absorbed by the rear substrate as the light travels through the rear substrate to the reflecting film.
Another improved backlight design proposed for liquid crystal displays is disclosed in Hathaway, Hawthorne, Fleisher, "New Backlighting Technologies for LCDs", Society for Information Display, International Symposium, Digest of Technical papers, Vol. XXII, pages 751-754, May 6-10, 1991. The Hathaway et al. backlight is a flattened tubular fluorescent lamp that has been bent at several points to form a serpentine-like tube structure. A problem with this design is the substantial non-uniformity of brightness. Shadow effects or light discontinuities exist at each barrier between adjacent arms of the serpentine-like tube structure which produce non-uniform brightness. The brightness uniformity of the Hathaway et al. backlight is less than that for the Hinotani et al. design. Further, the Hathaway et al. backlight utilizes a larger and more cumbersome structure of discrete components apparently without the possibility of integrated construction.